In the recovery of metal values from ores, such as sulfide ores, the ore is typically crushed, wet ground and classified as to particle size. The ground and sized ore is then slurried with additional water, if required, to form a pulp and the pulp is thereafter conditioned for flotation. After flotation, the separated float or mineral concentrate typically is further processed for recovery of the metal values in the concentrate. Of course, there is a metal value in the concentrate below which metal recovery therefrom becomes uneconomical. For example, in lead concentrates, if the level of lead is below about 45%, the recovery of lead therefrom becomes generally uneconomical and the concentrate is considered to be a low grade concentrate. Such low grade concentrates may, of course, be subjected to additional flotation to further enhance or upgrade the quality of the concentrate so that it may be economically processed for recovery of the metal values therefrom. Unfortunately such subsequent separation and processing can be inefficient and expensive. This is so, for example, with lead concentrates containing galena, pyrite, sphalerite and chalcopyrite. Also, the reagents that are used in such processing of low grade concentrates are more expensive and in some instances present environmental hazards which further increase the costs of processing the low grade concentrates so as to upgrade it.
Many clays and ores have been upgraded by use of magnetic separation techniques. Examples of such methods and apparatus for use in such methods are set forth in the following U.S. Pat. Nos.: 3,826,365; 3,887,457; 4,116,829; 3,853,983; 3,902,994 and 3,289,836. In each instance the materials being separated have widely different magnetic properties and in most instances one of the materials is present as an impurity, i.e., at exceedingly low concentrations.
In sulfide concentrates, such as lead concentrates containing galena, pyrite, sphalerite, molybdenite, and chalcopyrite, the minerals in the concentrate have substantially similar paramagnetic properties. Thus, it has not been possible to separate these concentrates by high gradient magnetic separation techniques due to the problems related to the magnetic matrix saturation and entrapment of unwanted particles. Consequently, there remains a need for separating mixtures of particles of substantially similar paramagnetic properties.